Study of nonuniform in-plane and in-depth residual stress of friction stir welding

Friction stir welding (FSW) is a newly developed welding technique that can join aluminum alloys of low fusion weldability. The conventional hole-drilling method does not consider the nonuniform in-plane stress around the drilled hole, it is no longer valid for the residual stress of FSW which has high stress gradient. However, assuming the relaxation of in-plane nonuniform residual stress to be uniform on a small increment of the boundary of the hole, the recently developed Moiré interferometry incremental hole-drilling (MIIHD) method can be used. Residual stress of a thin plate of friction stir welded aluminum alloy was studied by MIIHD. The longitudinal residual stress distribution in the transversal direction and through the thickness was obtained and compared with results by strain gage method.